The present invention relates to a nickel alloy sputtering target for forming a barrier layer and a nickel alloy thin film capable of inhibiting the diffusion of Sn as the component of a Sn solder or Sn—Pb solder between a substrate such as a semiconductor wafer or electronic circuit or a substrate layer or pad of the wiring or electrode formed thereon, and a Pb-free Sn solder or Sn—Pb solder bump formed thereon.
Generally, an aluminum or copper electrode or pad is formed on a semiconductor wafer or electronic circuit, or on the substrate thereof, and a conductive solder bump, Au bump, nickel bump or the like is additionally formed thereon. Among the above, a solder bump is the current mainstream material since it is easy to install and easy to repair.
Nevertheless, since an electrode substrate layer or pad formed from copper or the like easily reacts with a Pb-free Sn solder or Sn—Pb solder, after the solder bump is formed, there is a problem in that Sn diffusion will occur due to the heat arising in the manufacturing process or usage environment, a reaction will occur with the electrode substrate layer or pad formed from copper or the like as the substrate, and the characteristics will deteriorate due to the separation of the electrode layer or pad, or diffusion of the solder in the elements.
Due to the foregoing reasons, a proposal has been made for forming an intermediate barrier layer, via the sputtering method, capable of preventing the reaction between a substrate or an electrode substrate layer or pad formed from copper, and a Pb-free Sn solder or Sn—Pb solder bump.
A prerequisite of this intermediate barrier layer is that it has excellent adhesiveness with a substrate or a copper electrode substrate layer, and the wettability of the Pb-free Sn solder or Sn—Pb solder bump is excellent.
Nickel has been selected as this kind of material. Nevertheless, since nickel is a ferromagnetic material, it has inferior sputtering efficiency, and the nickel target must be made extremely thin in order to improve the sputtering efficiency. Thus, there is a problem in that the manufacture of this target is complicated, the target life is short, the target must be exchanged frequently, and, as a result, the manufacturing cost is increased.
Thus, a Ni—Cu alloy series film has been proposed as a material for reducing the magnetism of the Ni target and improving the sputtering efficiency (e.g., refer to Patent Document 1 and Patent Document 2). Nevertheless, this Ni—Cu alloy film does not necessarily have sufficient Sn barrier properties, and there is a problem in that it would react with the substrate film and increase electrical resistance.
As described above, since there is no sputtering target material capable of forming an effective barrier layer to become the intermediate layer with excellent solder wettability, when using a Pb-free Sn solder or Sn—Pb solder bump, problems often arise in that a reaction with the substrate or substrate copper layer would occur.
Meanwhile, in order to improve the adhesion with a ceramic substrate, a proposal has been made to use a nickel alloy target in which Mo, V and W are added to Ni (e.g., refer to Patent Document 3, Patent Document 4 and Patent Document 5). Further, a proposal has been made for using nickel alloy with Ti added thereto in order to improve the Sn barrier characteristics and to improve the etching characteristics (refer to Patent Document 6).
Nevertheless, although these are able to form a Ni alloy target and Ni alloy thin film, these are insufficient as a sputtering target capable of forming an effective barrier layer to become the intermediate layer with excellent solder wettability.    [Patent Document 1] Japanese Patent Laid-Open Publication No. S54-24231    [Patent Document 2] Japanese Patent Laid-Open Publication No. S56-110230    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2000-169922    [Patent Document 4] Japanese Patent Laid-Open Publication No. 2000-169957    [Patent Document 5] Japanese Patent Laid-Open Publication No. 2000-169923    [Patent Document 6] Japanese Patent Laid-Open Publication No. 2001-11612